Electrodeposition of bright copper-tin alloy



Patented Nov. 3, 1953 LEc'rRonEPosIrIon: on union! GOPP R-T N. ALLQY Qharles L. Faust and Wilbur G; Hcspenheide, Columbus; Ohio, assignors, h s message assign-e ments, t e City A e S amnies; Gammon Toledo, Ohio, a corporation of; Qhia No Drawing. Application June 11, 19519, Serial No. 98342 11 Claims. (01. 20 444.

This invention is generally described with reference to copper-tin alloy plating. In particular, this. invention relates to a bright. copper-tin alloy plate, to a method of plating bright coppertin alloy, to a composition useful in the process of producing a bright copper-tin plate, and to an article having an electroplated bright copper-tin alloy thereon. Specifically, this invention relates to the. continuous co-electrodeposition of copper and tin as a bright, hard, adherent, speculum metal.

Speculum metal, the well-known alloy containing 55 to 66 per cent copper and the balance tin, has long been known for its excellent resistance to tarnishing and for its pleasing white color. Of all the white metals that are now known, among those of non-noble metal quality, speculum is the closest in approach to the color of pure silver. Although pure silver has the best reflectivity of any of the metals, it soon loses its advantage in that respect because of tarnishme. On the other hand, speculum metal, although having almost the same reflectivity as pure silver, retains its initial reflectivity, and after a few hours of exposure, it will have much better reflectivity than silver because speculum metal does not tarnish. This relationship is well known to those skilled in the art. As speculum metal is a brittle material, it is difiioult to make shaped parts from the solid metal. Thus, it has been the practice to electrodeposit the speculum metal on the surface of articles made from other metals and alloys which were fabricated into the desired shape and form before plating. The copper-tin alloy electrodeposited from the baths of the. prior art is a dull, or at best, only a semi: bright mat finish. The prior art. baths have employed tin in the oxidized or stanniev form in the presence of copper in, the cuuric or cuprous form. In order to produce the pleasing appearance of the speculum metal, the mat. copperetin alloy coatings electrodeposited from the prior art baths must then be buffed and colored. Although this copper-tin alloy plate is relatively hard, it can nevertheless be bufi d to an attractive fi sh. The relative costs of buffing a mat or semi-bright plate, compared with the costs of using a bright 'ele'ctroplate, are well known to those in the metalflnishing industry. For reasons oi economy in manufacturing, t at to p ovide savin s .in

finishing costs and a reduction in the total number ofsteps in the finishing cycle, bright electroplates. are to be preferred. Thus, it.v becomes ap: parent that. a bright speculum or other coppertinalloy electroplate is highly desirable and would possess economical advantages. in metal finishing.

It is, therefore, an object of this invention to prov-idea method for co-electrodepositing copper and tin as a bright alloy characterized by the fact that it does not require. bufiing or coloring to, enhance its brilliance.

It is yet another object of this invention to provide. a process for electrodepositing speculum metal or other alloys of copper and tin.

It: is a still. further object of this invention to provide a composition useful in a process for coelectrodepositing a copper-tin alloy having the aforementioned improved qualities.

It is a til iur er Object of is n ent to nmv de n adheren e de o cu u m al o o h r brigh a o p ate f per an tin.

t s ga n n qbieq of th invention to p o.- vide an article having on its surfaces abright electrodeposited coating of copper-tin alloy.

These and other objects of the invention will 9. 1 m r a par t f t el o -ins de tai ed s pt on a d ex p It has now be n found h copperv and n c n be eo-deposited directl as an alloy and particularly as bright speculum metal on a basis material from mildly alkaline, stable electrolytic baths containing a soluble alkali cuurous com.- plex, a, soluble alkali stannous complex, an ex-. cess of y qnhesnhate, a p lyp p ide and an alkal th phesp at In, neral, the invention disclosed herein cone te ates e use f a l n e ials as the cathode which will receive speculum plates. Separate anod s QQPPE and i r p e a used although especially uniform operating re; sults are ebtained by employing the double anode sy tem at pure tin nd op eh n alloy tqn ai n p ta 1.5. per e n-ba an e c pper: The els t elv is h th has a 0f from. T-.5 21 5 and h e s qi sel d the b t an alkali tvaaide empress cyanid an e s of alka pvrophe phata sulia e, an alka t be phosphate and an organic colloid. An electric current is then passed from the anodes through the bath to the cathode to create a current density at the cathode not in excess of 90 amps/sq. ft. while maintaining the potential drop between the copper and tin anodes within the range of from 1 to 2 volts and the temperature of the bath not in excess of 190 F. The plate as deposited from this electrolytic bath is a bright alloy of essentially pure coelectrodeposited copper and tin. Very minor amounts of impurities are probably present in the electrodeposited coating and bath of this invention although the precise kind and quantity of impurities are unknown; however, they do not appear to materially affect the resulting bright copper-tin alloy. Whenever, due to a change in the amount of bath constituents or factors or in operating conditions, an increase in the copper content of the alloy plate occurs, there will be a corresponding decrease in the tin content so that there are always essentially only two elements present, i. e., copper and tin. Like-= wise, where there is a decrease in the copper content, there will occur an increase in the tin content of the plate. By varying the bath con-- stituents or factors and operating conditions, as will be hereinafter more clearly set forth, it is possible to deposit coatings containing from 5 to 95 per cent copper and the balance tin. A plate having less than 5 per cent copper is dull or at best semi-bright, whereas one having from 5 to 40 per cent is lustrous and silvery in color. A plate containing from 40 to 60 per cent copper is bright (specular) and white in color, including bright speculum metal, and one of from 60 to 85 per cent copper has a bright pink color. From 85 to 95 per cent copper content produces a mat coppery color and 95 to 100 per cent copper produces a dull red.

From 8 to 300 grams per liter of potassium pyrophosphate are dissolved in water to provide an excess of alkali pyrophosphate in relation to the other bath constituents. The preferred range is from about 40 to about 90 grams per liter.

The required amount of cuprous copper is added to the bath in the form of cuprous cyanide, or other cuprous salt along with the required amount of potassium cyanide. In the bath solution, it is thus believed that the copper exists as a soluble alkaline cuprous complex, i. e., a soluble potassium cupro-cyanide complex. It is also possible to form a soluble cuprous complex by adding a cuprous halide, such as the chloride or iodide for example, and the corresponding alkali salt, for example potassium chloride or iodide. A negligible, if any, amount of copper may exist in a pyrophosphate complex. It has been found that from about 2 to about 230 grams per liter of cuprous cyanide and from about 2 to about 350 g./l. of potassium cyanide, where the potassium pyrophosphate concentration is from 8 to 300 g./1., will provide the proper concentration of the potassium cupro-cyanide complex in the bath. It is preferred, however, to use from 15 to 80 g./l. of cuprous cyanide and from 22 to 120 g./l. of potassium cyanide in the bath.

The required amount of tin is added to the baths in the form of a tin salt such as stannous sulfate, chloride, or pyrophosphate. It is believed that the tin exists in the bath as the soluble alkaline stannous complex, i. e., the soluble potassium stannous pyrophosphate complex, regardless of the anion with which it m g be added as a stannous salt. If any stannic tin is present, its concentration is very minor and not critical in the baths of this invention. From about 2 to about 50 g./l. of stannous sulfate provide the desired concentration of the stannous complex in the bath. It is desirable, however, to add from 5 to 15 g./l of stannous sulfate to the bath, where the pyrophosphate is present in an amount of from 40 to g./l., so that this constitutes a preferred range.

Orthophosphate is added to the bath as potassium orthophosphate. The mono-, di-, or tribasic potassium orthophosphates can be used since the adjustment of the bath pH will result in the same end product, i. e., the conversion of these phosphates to the monobasic orthophosphate form. The orthophosphate does not cause precipitation of either stannous or cuprous compounds and with the glue at the specified pH ranges causes bright deposits of copper-tin alloys to be obtained. It is used in the bath in an amount of from about 5 to about g./1. per 8 to 300 g./l. of alkali pyrophosphate, although it has been found desirable to use orthophosphate in the range of from 10 to 30 g./1. when the pyrophosphate compound is present in an amount of about 40 to 90 g./l.

A colloid or soluble addition agent such as a polypeptide or more specifically a protein, is, as stated above, also a necessary ingredient of the baths for producing bright copper-tin alloy and speculum metal plates. Amino acids, and their derivatives and mixtures thereof, can likewise be used. Glue and gelatin have been found eminently successful in the baths of this invention, although many other proteins are also applicable. Generally, the glue or gelatin is added as a suspension in water. To be immediately effective in the bath, this suspension should be prepared several days in advance. Alternatively, this aging period can be eliminated by partially hydrolyzing the glue or gelatin. This hydrolysis is conducted by refluxing a suspension of glue or gelatin in an acid or alkaline solution. After hydrolysis of the glue solution, the pH thereof may be adjusted in the range of from '7 to 10 before adding to the bath. From about 0.01 to about 5.0 g./l. of glue per 8 to 300 g./l. of pyrophosphate provides a satisfactory concentration in the bath, although it is preferred to use from 0.5 to 2.0 g./l. of glue.

The pH of the bath is adjusted by adding a suitable acid, such as orthophosphoric or pyrophosphoric acid. If stannous sulfate has been used in making up the plating bath, sulfuric acid can also be used when it is necessary to reduce the pH. Where it is necessary to increase the pH in order to adjust or raise it to the desired value, potassium hydroxide can be added to the bath. Two precautions should, however, be observed. If the pH of the bath exceeds about 10.5 for any appreciable period of time stannous hydroxide, which is very diflicultly soluble in the bath, will be precipitated, reducing the concen tration of the stannous pyrophosphate complex. Thus, the bath will be thrown out of balance and the composition of the plate will be altered. Similarly, if the pH of the bath is less than about 6.5 for any appreciable time, difiicultly soluble cyanide salts will be precipitated, resulting ina loss of cyanide and changing the concentration of the soluble cuprous cyanide complex. This, too, alters the desired ratio of constituents in the bath and also "the appearance and compositions! the plate. Hence, it follows that "to maintain the stability of the cuprous cyanide-stamens pyrophosphate electrolytic bath, in order to continuously plate bright speculum metal or other alloy of copper and ti it is necessary to maintain the pH of the bath within the range of from 6.5 to 10.5, and preferably in the range :of trom 7 to 9.5.

In the electrolytic bath used in this process of electro depositing a bright copper-tin alloy, equivalent sodium salts or bases can be used wherever potassium salts or bases are disclosed. Furthermore, equivalent ammonium salts or bases, i. e., those containing the ammonium radical,

NHI

can also be used without significantly altering the results obtained. For the purposes of this invention ammonium salts and bases are to be considered as included with the sodium .and potassium salts and basesshown above,

Moreover, the corresponding carbonates can likewise be used in full or partial replacement of the hydroxides when adjusting the pH or to minimize changes due to absorption of carbon dioxide from the atmosphere. If not added they will form, as in the instance of all alkaline baths, by carbon dioxide absorption from the atmosphere. Excessive concentration of carbonate lowers the anode and cathode ef iciencies which, for some plate compositions may be desirable. The carbonate concentration should, however, not exceed 120 g./l.

As stated above, minor amounts of impurities may be present in the bath and resulting plate, although their presence and amount are not precisely known. However, While not absolutely necessary, it is naturally desirable that the materials used in the process disclosed herein should be substantially pure in order to decrease the amount of possible contaminants and to obtain reproducible results. It is, thus, to be preferred to employ chemically pure, or the C. P. grade of materials, whenever possible when practicing this invention.

The electrolytic baths used to make the bright speculum or other bright copper-tin alloy plates of this invention can be advantageously prepared by a number of methods. For example, one method is to dissolve the desired quantity of cuprous cyanide in a solution of potassium cyanide. The required amount of stannous sulfate is next dissolved in a solution of potassium pyrophosphate. These solutions are then mixed, followed by the addition thereto of the necessary amounts of potassium orthophosphate and glue. The pH of the resulting electrolytic solution is finally adjusted to the desired value by the addition of acid or alkali. Alternatively, the electrolytic bath can be prepared by dissolving the required amounts of the constituents in water in the following order: potassium pyrophosphate, potassium cyanide, cuprous cyanide, stannous sulfate, potassium crthophosphate and glue. The pI-l of the bath is then adjusted to the desired figure by adding appropriate amounts of acid or alkali. A third method is to mix all of the bath c n i e except the glue, in the dry state by any known means to obtain a homogeneousappearing mixture of dry solids. This mixture is then dissolved in the required amount of water, followed by the addition of the. glue. If neces- 6. sary, the pH can be adjusted to the desired range by appropriate additions of acid or alkali.

The bright plating baths disclosed herein are stable at operating temperatures up to the boiling point of the solution; however, the optimum operating temperatures usually do not exceed 190 F. The preferred temperature range is from to F. During the plating process an increase in temperature within this range equal-- izes the anode and cathode current efliciencies so that the proper dissolved metal balance in the bath is maintained during continuous operation.

Operatingcathode current densities of up to 90 amps/sq. ft. or more can be used in this process for producing speculum metal plates. It has been found best to employ current densities not in excess of about 50 amps/sq. it. and preferably in the range of from 10 to 40 amps/sq. ft. By varying the current density, the agitation and temperature, the composition of the bright copper-tin alloys can be varied somewhat. The customary methods known to the art for cleaning, degreasing and pickling can be used in preparing a metallic (or non-metallic) surface for receiving the speculum plate or other alloy plate of copper-tin. The surface of the basis material or cathode being now in a cleaned condition, can be directly plated with the speculum metal of this invention. The articles to be plated as the cathodes can be made of iron, steel, nickel, copper, brass, zinc, zinc die castings or alloys and aluminum, as well as many other materials normally used and on which it would be desirable to plate speculum metal. If desirable, the basis material may also be strike-plated with copper, nickel, silver, etc. by electroplating prior to depositing thereon the bright'speculum alloy coating of copper and tin of this invention.

Separate soluble anodes of copper and of tin are preferred, employing two anode bus bars to which the electric current is separately adjustable. Alloy anodes of the same composition can be used for plate compositions containing up to 15 per cent tin. With higher percentages of tin, alloy anode dissolution is irregular and composition control of the solution is difficult to maintain.

Satisfactory, continuous operation can also be efiected through the use of insoluble anodes, such as iron, nickel, or other suitable conductor with pure tin and pure copper anodes or copper-tin alloy anodes containing up to 15 per cent tin and the balance copper. Where part of the current is carried by the insoluble anodes, they lower the total efficiency of the copper and tin anodes so that the tin concentration is kept constant.

Moreover, it is also possible to use insoluble anodes entirely in plating bright copper-tin alloys, as disclosed in Examples 1 and 3, infra. Such procedure, however, is not recommended because of the problems entailed in maintaining the proper balance of the plating bath. Thus, where there is no anodic replenishment, the alloy deposited on the cathode will be taken directly from the bath. This necessitates constant inspection of the bath to maintain the bath constituents in the proper ratio, considerably reducing the ease and economy of the plating process. Operation with insoluble anodes might also cause oxidation of the stannous tothe stannic form of tin, which is not desirable in the bath.- Although stannic tin is not too harmful as such, nor does it harm the plate as is well known for stannous tin in the stannate tin plating bath and the copper cyanide sodium stannate plating bath,

the elimination of the stannous tin of the bath serves to upset the operating characteristics of the bath.

. Current densities for each anode can range up to 30 amps/sq. ft., although it is preferred to maintain the individual current density of each anode within the range of from 1 to amps./ sq. ft.

By properly adjusting the ratio of the area of the copper anode to the tin anode, the ratio of copper and tin dissolution, and also their rate of dissolution, can be balanced against the deposition rate and ratio of these two metals on the cathode so that the concentration of copper and tin in the electrolytic bath remains substantially constant. It is also necessary, in order to control the dissolution of the anodes, to have a voltage drop of from 0.5 to 2 volts between the copper and tin (or the copper and copper-tin) anodes. Furthermore, this voltage drop, determined by the geometry of the plating cell, should not appreciably exceed 2 volts to prevent the deposition of copper and/or copper-tin alloy on the tin anode. To prevent tin from depositing on the copper anodes by immersion and to operate the copper anodes at less than 100 per cent efficiency, usually to 80 percent, the copper anode to cathode voltage during bright plating should be in the range of from 2 to 3 volts. The upper limit can vary above 3 volts, of course, depending on the distance between the anodes and cathodes. The upper limit on the tin anode to cathode voltage is determined by the appearing of the undesirable reactions Sn- Sn+ and Sn+ Sn+ because Sn+ does not produce bright or speculum metal plates. The lower limit is set by the requirement that copper should not deposit on the tin anodes by immersion. Thus, it has been found necessary to maintain the tin anode to cathode voltage from 0.1 to less than 2 volts 1 where the copper anode to cathode voltage is from 2 to 3 volts. The tin anode to cathode voltage range can, of course, be increased as the copper anode to cathode voltage is increased.

The time during which the process is carried on relates only to the thickness of the speculum plate to be deposited on the cathode, as will be obvious to those skilled in the art.

Some loss occurs during the plating operation. For example, the copper and tin anodes must be inspected at regular intervals and replaced before being entirely exhausted to prevent disruption of the bath stability. The only other appreciable losses occurring from the electroplating operation will be some loss of cyanide by reaction with carbon dioxide in the air and minor amounts of the other bath constituents removed in the solution film clinging to the plated work. These small dragout losses can readily be controlled by periodic checks of the bath constituents which will indicate the amount of constituent needed to maintain the bath in the proper balance and within the desired operating ranges. It is thus seen that the bath can be continuously operated, for it is generally only necessary to replace the soluble anodes if used or bath constituents if insoluble anodes are used. Concentrations of undesirable reagents or chemicals do not build up in the bath during the process to slow down the plating operations, to impair the plates, or to require that the bath be dumped and entirely replaced with new materials.

Within the ranges of concentration of chemical constituents and operating conditions as de- 8 scribed herein, bright speculum and other copper-tin alloy coatings will be readily produced.

The following example will serve to illustrate the invention with more particularity to those skilled in the art:

EXANCPLEI An electrolyte was prepared containing the following ingredients:

Components: Amount Potassium cyanide (KCN) 25.0 g./1. Cuprous cyanide (C112(CN)2) 18.8 g./1. Potassium pyrophosphate (K4P2O7.3H2O) 40.0 g./1. Stannous sulfate (SnSOr) 10.8 g./1. Potassium orthophosphate (KH2PO4) 7.0 g./1. Hide glue 0.1 g./1.

Balance water.

The pH of this bath, as measured by a glass electrode, was about 9.0. The bath was brought to an operating temperature of F. and a stel cathode and insoluble steel anodes inserted therein. A potential of 3.8 volts gave a cathode current density of 30 amperes per square foot. The bath was then operated for ten minutes and resulted in a deposit on the cathode of bright speculum alloy plate, 54 per cent copper and 46 per cent tin.

Three control runs were also made. In the first control run, a bath was prepared and operated exactly like the above except that no hide glue and no potassium othophosphate was added to the bath. The bath had a pH of about 8.2. The resulting plate was coppery colored and so spongy that it was easily rubbed off. In the second control run, glue was omitted from the bath. The resulting plate was dull and showed treeing. For the third control run, only potassium orthophosphate was omitted from the bath. After plating for ten minutes, a deposit was obtained which was semi-bright. After the bath stood idle for '72 hours, the next deposit was mirror-bright which was believed to be due to a very small amount of orthophosphate ion being present from hydrolysis of pyrophosphate at the pH used. This was proven by the results obtained with the bath shown in the first part of the example above.

Other examples of electrolytic bath compositions and operating conditions that may be employed in the practice of this invention to produce imiform mirror-bright, white speculum and other alloy plates are as follows:

Balance water.

Temperature F., pH 10, and cathode current density of 15 amps/sq. ft. Separate copper and tin anodes, brass cathode. The resulting plate contained 52 per cent copper and 48 per cent tin and was specular.

:6 EXAMPLE 7 EXAMPLE 3 praw ep m v p H 9.5, andoathode cur-- ree de si y. 40 ..am

Balance water.-

- ./sq. ft. K Steel cathode,

Temperature 160 pH 9', and cathode current density of 30arnp's/sq. ft. Steel anode, zine bronze alloy and tin anodes. Bright speculum 60 per cent copnmgl pef-halane tin; were produced with this bath.

plates conta frorn 55 to die casting cathode. The resulting plate @655 tained 54 per cent copper and 46 per cent tin andwas mirror bright.

ndditional experiments were condueted using e baths and prqcesses of this invention. tain bright plates.

t In thehaths, Nos. 1 to 54, f b e Ab w th pyrophosphate was 9 EXAIVT 4 ect of Monobasic potassiumorthop'hos the composition on the resulting plate:

CONDITIONS The data in Table A reveal the importance of operating conditions and concentrations of glue and orthophosphate in these baths and how they can be varied over a considerable range and yet produce adherent hard plates of copper-tin alloys.

Not only can the operating conditions, orthophosphate, and glue be varied, but the ratio of copper to tin in the baths can also be varied to produce plates having different amounts of copper and tin present. For example, baths were prepared containing 90 g./l. of potassium pyrophosphate, 16 g./l. of potassium cyanide, 20 g'./l. of monobasic potassium orthophosphate, and 1 'g./l. of hide glue. The amounts of cuprous cyanide and stannous sulfate were then varied for each bath, although th total amount of both of these two constituents did not exceed 20 g./l. The pH of the baths was adjusted to 9.0. The baths were then operated at a temperature of 180 F. and cathode current density of 30 amps/sq. ft. The results obtained in the composition of the plates by thus varying the ratio of cuprous copper to stannous tin in the baths is shown in Table B, below:

Table B EFFECT ON PLATE COMPOSITION DUE TO VARIA- TIONS IN RATIO OF COPPER TO TIN IN THE BATH Copper to Percent of Percent of tin ratio copper in tin in in bath plate plate like white metal deposits are then, as hereinabove described, obtainable. It is apparent from Example 1 that the simple combining of the two complex metal salts does not necessarily produce a bright plating bath, but that owing to the pH range that can be realized with the cuprouse cyanide, stannous-pyrophosphate solution, a small amount of glue and orthophosphate dissolved in the solution can so regulate the codeposition process as to give lustrous, bright or specular alloy plates of copper and tin.

Furthermore, one important hypothesis to explain the mechanism of bright metal plating is based upon the phenomenon of partial precipitation at the cathode surface. In other words, the cathode film, because of removal of ions by electrodeposition and by simple diffusion, has a composition that is difierent from the body of the electroplating bath. With the proper concentration and combination of dissolved components and of pH in the bath, the cathode film will assume a slightly different pH, at which value some constituent will momentarily precipitate and thereby influence the deposition process to produce a mirror-bright plate. It is believed that the operating pH values are very close to those at which some constituent of the plating bath will precipitate as a compound in the cathode film and at or near the cathode surface. Upon attempting to apply such reasoning to solutions for codepositing copper and tin, the fact is encountered that such solutions as have been used heretofore have relatively high pH values, which are necessary to keep the tin in solution or which involve the use of cupric or stannic salts. Thus, no depositing mechanism can be expected to produce precipitation to assist a brightening action by an increase in the pH of the cathode film. On the other hand, this invention discloses that, in the presence of cuprous and stannous complexes within a pH range of 6.5 to 10.5, the small concentrations of orthophosphate added to the bath or from hydrolysis of the pyrophosphate at this pH, and also glue are essential for setting up the conditions in the cathode film for depositing bright copper-tin alloys.

, Most generally, the dense, uniform and bright speculum plate of this invention will be desired for decorative purposes, relying upon its appearance without any further plating or finishing operations. However, if it is so desired, other bright metals, such as bright nickel and/or chromium, can be deposited directly on this bright speculum metal plate. A particularly important attribute of the present process is its ability to bright-plate an alloy of copper and tin directly on zinc die castings without the need for one or more strike plates as is required when using other baths, which, due to their strong alkaline or acidic nature, readily attack the zinc alloy. In a process involving a single plating step, zinc die castings can be finished to an attractive bright, whitemetal appearance, which is retained indefinitely and which has been found to possess important protective qualities relative to the customary composite plate of copper, nickel, and chromium on zinc die castings. The bath of the present invention has excellent throwing power and attributes for electrodepositing copper-tin alloys in a wide range of compositions, and the process can be practiced for other purposes than merely decorative plating. Thick plates, for example, 0.030 inch have been satisfactorily deposited with mirror-like appearance without noticeable treeing or roughness.

In summary, this invention teaches that bright, lustrous and speculum metal alloy plates of copper and tin can be readily electrodeposited on a basis material from a mildly alkaline bath containing a cuprous complex, a stannous complex, a cyanide, an orthophosphate, a pyrophosphate, and an addition agent such as a polypeptide. The composition of the bath and the operating conditions and elements can be varied over a wide range to obtain bright and/or speculum metal platesand the bath can be operated continuously to 7 plate copper and tin. Although copper is present in the prior art baths in the cupric or cuprous forms, tin is present therein in the oxidized or stannic form and such baths have not been found suitable for producing bright speculum or other copper-tin alloy plates. Thus, the present invention involves the novel feature of combining cuprous copper and stannous tin salts in a relatively stable solution which can be used to produce bright speculum and other copallo slates. nother and feature of n eseat' ar n iq iisth' 6 may ,h tas. all.

in these bat s W hb t 'i' seatin th r u o s r's aaag s commas a d tha such Q th nhqs a e ans else as. h activ g ene ad ie i ns re ne sa t p r e' r eh lustrous, pasms meta and other cqnsehtih a loy late "Si 'ce aricms ss ble e b d ie s ul be made in the n n nj re n de cr b d, d s ce man screet c anges an he made n, h h di ent abo e et. or h n is :91 be, ns t os hat al mater a d sclo ed, is m b nterpreted as. lusira re a n in' a imi ng, sense;

Ha g h sde c ih he, n en on, What s. a med. s new n nP and, s des r d, be secured by Letters Patent, is

1, An aqueous bath useful in the coelectros o i r c rne n al y and; ha n a of from 7 toll), consistingessentially' or an alkali cyanide, an alkali orthophosphate, cuprous cyanide, stannous pyrophosphate, a 'material selebted'fromthe group consisting ofglue, gelatin, and hydrolysis products thereof, an excess of alkali pyrophosphate, and water.

2. The process of electrodepositmg an alloy of copper a d tin, comprising passingan electric current from an anode to a cathode through an electrolyte having a'pH of from; 6.5 to 10.5 and consisting essentially oi a cuprous compound sel ted from the. rqun cons s f upr us cyanide and halide, a stannous compound selected from the group consisting of stannous chloride, pyrophosphate, and sul fate, a cyanide selected from the group,consistingotammonium, sodium, and pptass ium cyanide, an excess of alkali pyro- HhQSD hate, a material selected irom the, group consisting of; glue, gelatir' and hydrolysis products, the s'q an lka i lr hon phate- '3', The process of electrodepositing a bright alloy of copper and tin on a basis metal, comprising making the basis metal' the cathode, in anelectrolyte having a pH offrom '7 to 9 .5. and consisting'essentially of cuprous cyanidfi, stannous pyrophpsphate, an ex 'c sess. or alkali, pyrophosphate, an alkali orthophosphate, an alkali cyanide, a material selected from the group consisting of glue, gelatin, and hydrolysis products thereof, and water, passing an electric current from the anode to said cathode through said electrolyte to create a current density at said cathode of from 10 to 90 amps/sq. ft. while maintaining the electrolyte at a temperature not in excess of 190 F.

4. A solution for plating an alloy of from 5 to 95 per cent copper and the balance tin on a basis material, having a pH of from about 6.5 to about 10.5 and comprising essentially from 8 to 300 grams per liter of a pyrophosphate compound selected from the group consisting of ammonium, potassium and sodium pyrophosphates, from 2 to 230 grams per liter of a soluble cuprous compound selected from the group consisting of cuprous cyanide and halide, from 2 to 350 grams per liter of a cyanide selected from the group consisting of ammonium, potassium and sodium cyanides, from 2 to 50 grams per liter of a soluble stannous compound selected from the group consisting of stannous chloride, pyrophosphate and sulfate, from 5 to 120 grams per liter of an orthophosphate compound selected from the group consisting of ammonium, potassium and sodium mono-, di-, and triorthophosphates, from 0.01 to 5.0 grams per liter of a material selected from the group consisting of glue, gelatin, and hydrolysis products thereof, and water.

5., electrolyte ior electroslemsit ln l iron-5 o 951m n Q P Q an t e b a he a an alloy, having a pH oi from 7 toiland co isr ing essentially from $0,129 grams per liter of a pyrophosphate selected from the group Q01]: s st n of aniz cn u ,v pot s u a d s dium nyrQphQsphates, from 15 to, 80 grams per liter of, a soluble cuprous compound selected from the group consisting of cuprous. halide and cuprous cyanide, from 22 to grams per liter of, a cyanide selected from the group consisting, 0,15 ammonium, potassium andsodium cyanidea from 5 t l5igramsper liter of a, soluble stannous om pound selected from the group consisting of; stannous chloride, pyroph sphate and. sulfat rom 10 to 3.0. grams per liter of an orthophosphate compound selected from. the group consisting of ammonium, potassium. and sodium mQ o-, im and, triorthophosphates, from 0.5 to ;.0 grams per literv oi a material. selected from the group consisting 'of. gl e, gel t n an yd is prod:

ucts thereof, and water.

6. In the process, of continuously coelectro: depositing an alloy of from; 5 to. 95 per cent, cop,- per and the balance. tin: on a basis materiahthe steps consisting of making: said material, the cathode to be plated'in; an, electrolyte; consisting, essentially'of from 40gto;90;grams.-pen liter ot a py ophosphate o noundselectedfram hee-rounon ting. f mmonium. potassium. and: sodium pyrophosphates, from 15;;tm80 grams; pen literof a soluble; cuprous. cpmpdundiv selected. from; group consisting of cuprous; halide. and cuprous. cyanide, from 22' to.- 120igrams, per liter of a: cyanide compound selected -from thegroup: con sisting of ammonium, potassium, and; sodium cyanides, from 5 to 1 5* grams-perliter of a soluble stannous compoundfselected from the group con,-

i a n s gr qnh saha i iate and.

chloride, from, 101 ta 0. rams. per, liter of: an: rth p a e om ou l te rom he, rou p ls n of ammo ium potass m. nd sodium, mono-, di; and triorthopho sphates, from 55, 9 ,0 ra Her, it r i; ma e alL e ted; from the group consisting of glue, gelatin, and hydrolysis products thereof, and water, adjusting the pH of the electrolyte to from 7 to 9.5, and passing an electric current from said cathode to copper and tin containing anodes in a manner to create a current density at said cathode of from 10 to 40 amps/sq. ft. and at the anodes of from 1 to 15 amps/sq. ft. while maintaining the potential drop between the anodes of from 0.5 to 2 volts, the ratio of tin containing anode to cathode voltage from 0.1 to less than 2 volts where the copper anode to cathode voltage is from 2 to 3 volts and the temperature of the bath from to F.

'7. In the process of electroplating a basis material with an alloy coating having from 5 to 95 per cent copper and the balance tin, the steps consisting of immersing the basis material as a cathode to be alloy coated in an electrolytic bath having a pH of from 6.5 to 10.5 and comprising essentially from 8 to 300 grams per liter of a pyrophosphate compound selected from the group consisting of ammonium, potassium and sodium pyrophosphates, from 2 to 230 grams per liter of a soluble cuprous compound selected from the group consisting of cuprous cyanide and halide, from 2 to 350 grams per liter of a cyanide selected from the group consisting of ammonium, potassium and sodium cyanides, from 2 to 50 grams per liter of a soluble stannous compound selected from the group consisting of a stannous chloride, pyrophosphate and sulfate, from to 120 grams per liter of an orthophosphate compound selected from the group consisting of ammonium, potassium and sodium mono-, di-, and triorothophosphates, from 0.01 to 5.0 grams per liter of a material selected from the group consisting of glue, gelatin, and hydrolysis products thereof, and Water, passing an electric current from said cathode, in a manner to create a current density not in excess of 90 amps/sq. ft. at said cathode, through said bath to the anodes having a current density of up to 30 amps/sq. ft. with a potential drop between the anodes of from 0.5 to 2 volts, while maintaining the ratio of tin containing anode to cathode voltage from 0.1 to less than 2 volts where the copper anode to cathode voltage is from 2 to 3 volts and said bath at a temperature not in excess of 190 F.

8. A composition of matter consisting essentially of an alkali cyanide, an excess of alkali phyrophosphate, an alkali orthophosphate, a material selected from the group consisting of glue, gelatin, and hydrolysis products thereof, a cuprous compound selected from the group consisting of cuprous cyanide and halide, and a stannous salt selected from the group consisting of stannous sulfate, halide, and pyrophosphate.

9. An aqueous solution having a pH of from 6.5 to 10.5 and consisting essentially of a cuprous compound selected from the grou consisting of cuprous cyanide and halide, a stannous compound selected from the group consisting of stannous chloride, pyrophosphate, and sulfate, an alkali cyanide, a material selected from the group consisting of glue, gelatin, and hydrolysis products thereof, an excess of alkali pyrophosphate, and an alkali orthophosphate.

10. A composition of matter consisting essentially, by weight, of from 8 to 300 parts of a pyrophosphate compound selected from the group consisting of ammonium, potassium, and sodium pyrophosphates, from 2 to 230 parts of a soluble cuprous compound selected from the group consisting of cuprous cyanide and halide, from 2 to 350 parts of a cyanide selected from the group 1 consisting of ammonium, potassium, and sodium cyanides, from 2 to parts of a stannous compound selected from the group consisting of stannous chloride, pyrophosphate, and sulfate, from 5 to 120 parts of an orthophosphate compound selected from the group consisting of ammonium, potassium, and sodium mono-, di-, and triorthophosphates, and from 0.01 to 5.0 parts of a, material selected from the group consisting of glue, gelatin, and hydrolysis products thereof.

11. A composition of matter consisting essentially, by weight, of from 40 to parts of a pyrophosphate selected from the group consisting of ammonium, potassium, and sodium pyrophosphates, from 15 to 80 parts of a soluble cuprous compound selected from the group consisting of cuprous halide and cuprous cyanide, from 22 to parts of a cyanide selected from the group consisting of ammonium, potassium, and sodium cyanides, from 5 to 15 grams per liter of a stannous compound selected from the group consisting of stannous chloride, pyrophosphate, and sulfate, from 10 to 30 parts of an orthophosphate compound selected from the group consisting of ammonium, potassium, and sodium mono-, di-, and triorthophosphates, from 0.5 to 2.0 parts of a material selected from the grou consisting of glue, gelatin, and hydrolysis products thereof.

CHARLES L. FAUST. WILBUR G. HESPENHEIDE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,536,859 Humphries May 5, 1925 1,970,548 Batten et a1. Aug. 21, 1934 1,970,549 Batten et a1 Aug. 21, 1934 2,079,842 Cinamon May 11, 1937 2,216,605 Sklarew et al. Oct. 1, 1940 2,397,522 Baier Apr. 2, 1946 2,436,316 Lum et al. Feb. 17, 1948 2,468,825 Jernstedt May 3, 1949 2,511,395 Baier et al June 13, 1950 

1. AN AQUEOUS BATH USEFUL IN THE COELECTRODEPOSITION OF BRIGHT COPPER-TIN ALLOYS AND HAVING A PH OF FROM 7 TO 10, CONSISTING OF ESENTIALLY OF AN ALIKALI CYANIDE, AN ALKALI ORTHOPHOSPHATE, CUPROUS CYANIDE, STANNOUS PYROPHOSPHATE, A MATERIAL SELECTED FROM THE GROUP CONSISTIG OF GLUE, GELATIN, AND HYDROLYSIS PRODUCTS THEEOF, AN EXCESS OF ALKALI PYROPHOSPHATE, AND WATER. 